A lethal myeloproliferative syndrome in mice transplanted with bone marrow cells infected with a retrovirus expressing granulocyte‐macrophage colony stimulating factor.

Murine bone marrow cells infected with a novel recombinant retrovirus, MPZen(GM‐CSF), were engrafted into lethally irradiated recipients. The transplanted animals developed extremely high circulating levels of GM‐CSF (up to 3 x 10(5) units/ml), and greatly elevated peripheral nucleated cell counts (up to 110 x 10(6) per ml). Their haemopoietic tissues contained GM‐CSF proviral DNA and produced substantial levels of GM‐CSF. The mice died within 4 weeks of transplantation with extensive neutrophil and macrophage infiltration of the spleen, lung, liver and peritoneal cavity and significant infiltration of both heart and skeletal muscle by neutrophils, macrophages and eosinophils. The thymus and lymph nodes were deficient in lymphoid cells. No disease occurred when infected cells from haemopoietic tissues of the primary transplanted animals were injected into normal or sub‐lethally irradiated mice. Dysregulated GM‐CSF expression by haemopoietic cells thus produces a fatal albeit non‐neoplastic myeloproliferative syndrome.